Medical imaging technologies, such as Computed Tomography (CT), Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), and Magnetic Resonance Imaging (MRI) detect and record tissue responses in the presence of applied signals and/or injected or ingested substances, and generate visual representations indicative of such responses. This data can be analyzed to differentiate or monitor various types of tissue, and can be used to diagnose malignancies in the tissue.
In typical medical imaging techniques a volume of tissue is scanned within a region of anatomical interest. The acquired scan data can then be transformed into or reconstructed as a series of planar images or image “slices.” Any given image slice comprises an array of volume elements or voxels, where each voxel corresponds to an imaging signal intensity within an incremental volume that may be defined in accordance with x, y, and z axes. At any particular time, the intensity of an imaging signal associated with a particular voxel depends upon the types of tissues within an anatomical region corresponding to the voxel.
In some imaging applications, a contrast agent is administered to the patient to selectively enhance the imaging properties of a selected tissue type. In these applications, the intensity of the imaging signal can help to differentiate healthy from malignant tissue. Furthermore, the response of the tissue with respect to time following contrast agent administration is also useful in evaluating tissue. Temporally varying or dynamic tissue dependent contrast agent uptake properties, for example, can be used to identify particular tissue types, and to differentiate malignant from benign tissues.
Gadolinium DPTA and other contrast agents are often used in conjunction with MRI processes to improve the distinction between types of soft tissue, and particularly to distinguish malignant versus benign breast tumors or lesions. Normal or healthy tissue typically exhibits a background signal intensity in the absence of a contrast agent, while abnormal or tumorous tissue exhibits either a reduced, increased, or substantially similar signal intensity relative to the background intensity. Thus, prior to contrast agent administration, abnormal tissue may or may not appear different from normal tissue.
When a contrast agent is applied, in general a lesion will exhibit one of many types of time-dependent contrast agent uptake behaviors. Within imaging data corresponding to a time series of scans, each type of contrast agent uptake behavior manifests as a corresponding type of dynamic imaging signal intensity profile or curve. Each type of dynamic intensity curve probabilistically corresponds to whether the lesion is benign or malignant.
The imaging data acquired both before and after the administration of the contrast agent can therefore be provided to a computer for computer-aided detection (CAD) of cancer and other malignancies. The CAD system receives the acquired images, and calculates a set of measurements or features in the region of interest. Based on the calculated data, the CAD system categorizes tissue in the region of interest and provides a display to a user, typically a radiologist. The display typically includes both an indicator of a potentially malignant area and also a numerical parameter or rating, such as a percentage enhancement of the brightness of the tissue in the selected area.
In practice, most CAD system displays are readily interpreted by users. That is, a displayed detection is either accepted as malignant or is easily dismissed as a false positive mark due to some observable artifact in the image. However, users may desire more information about the region that was marked. Since CAD systems typically base display decisions on computed numerical scores from a plurality of measurements, there is no current method for providing feedback to a radiologist regarding why a particular image region was marked or not.
Therefore, there is a need for providing data to users indicating the factors influencing a CAD system's determination about whether or not to mark a particular region as a detection.